heron/api/src/java/com/twitter/heron/api/windowing/triggers/WatermarkCountTriggerPolicy.java

//  Copyright 2017 Twitter. All rights reserved.
//
//  Licensed under the Apache License, Version 2.0 (the "License");
//  you may not use this file except in compliance with the License.
//  You may obtain a copy of the License at
//
//  http://www.apache.org/licenses/LICENSE-2.0
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.
package com.twitter.heron.api.windowing.triggers;

import java.util.List;

import com.twitter.heron.api.windowing.DefaultEvictionContext;
import com.twitter.heron.api.windowing.Event;
import com.twitter.heron.api.windowing.EvictionPolicy;
import com.twitter.heron.api.windowing.TriggerHandler;
import com.twitter.heron.api.windowing.TriggerPolicy;
import com.twitter.heron.api.windowing.WindowManager;

/**
 * A trigger policy that tracks event counts and sets the context for
 * eviction policy to evict based on latest watermark time.
 *
 * @param <T> the type of event tracked by this policy.
 */
public class WatermarkCountTriggerPolicy<T> implements TriggerPolicy<T> {
  private final int count;
  private final TriggerHandler handler;
  private final EvictionPolicy<T> evictionPolicy;
  private final WindowManager<T> windowManager;
  private volatile long lastProcessedTs;
  private boolean started;

  public WatermarkCountTriggerPolicy(int count, TriggerHandler handler, EvictionPolicy<T>
      evictionPolicy, WindowManager<T> windowManager) {
    this.count = count;
    this.handler = handler;
    this.evictionPolicy = evictionPolicy;
    this.windowManager = windowManager;
    this.started = false;
  }

  @Override
  public void track(Event<T> event) {
    if (started && event.isWatermark()) {
      handleWaterMarkEvent(event);
    }
  }

  @Override
  public void reset() {
    // NOOP
  }

  @Override
  public void start() {
    started = true;
  }

  @Override
  public void shutdown() {
    // NOOP
  }

  /**
   * Triggers all the pending windows up to the waterMarkEvent timestamp
   * based on the sliding interval count.
   *
   * @param waterMarkEvent the watermark event
   */
  private void handleWaterMarkEvent(Event<T> waterMarkEvent) {
    long watermarkTs = waterMarkEvent.getTimestamp();
    List<Long> eventTs = windowManager.getSlidingCountTimestamps(lastProcessedTs, watermarkTs,
        count);
    for (long ts : eventTs) {
      evictionPolicy.setContext(new DefaultEvictionContext(ts, null, Long.valueOf(count)));
      handler.onTrigger();
      lastProcessedTs = ts;
    }
  }

  @Override
  public String toString() {
    return "WatermarkCountTriggerPolicy{" + "count=" + count + ", lastProcessedTs="
        + lastProcessedTs + ", started=" + started + '}';
  }
}